the answer may be in your last paragraph.

I think it has more to do with love, and respect. love fore life, respect for life. more love and respect can bring us more understanding of each other, less selfishness, more true friendships and support for each other through difficult times in life.

I don't think "self-discipline" is the problem here. on the contrary, I would imagine it should take quite some self discipline to execute a killing successfully like Lu Gang's case or Wang XiaoYe's case. also, those involved in the two cases are generall regarded as being "successful" in parents' eyes or in the eyes of others, before the tragedy. I would think it also needs quite some self discipline to reach that "successful" level before they snapped.